Extract

The few supposed gaseous unimolecular reactions are thermal decompositions of relatively complex molecules which occur in two or more stages. The course of the reactions can be followed by the rate of change of pressure in a closed system in which the decomposition is proceeding at some suitable temperature, and the experimental results may be explained kinetically on the assumption that the measured rate of reaction is determined solely by the slowest of the intermediate stages of the process. The usual criterion of a unimolecular reaction is the proportionality between the absolute rate of change and the first power of the concentration, and in this respect it is improbable that any complex process would survive the test over a wide range of pressures; for not only may the relative speeds of the consecutive stages be influenced by pressure but the actual course of the reaction may be changed.

Footnotes

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